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Agapanthus gall midge is a fly that can cause buds of Agapanthus to become deformed and discoloured and fail to flower. It was first noticed in the UK in 2014 but may have been present for several years.
Agapanthus gall midge is a tiny fly that lays eggs on the developing flower buds of Agapanthus. The feeding activities of the larvae inside the buds cause abnormal bud development and infested buds usually fail to open.
Until 2016 the species of midge causing this problem was undescribed (i.e. new to science). Consequently, very little is known about the biology and lifecycle of this insect. The Plant Health team at RHS Garden Wisley have been studying the midge since its discovery in 2014, and are asking for help from gardeners who have seen agapanthus gall midge or damaged flowers.
By Post: Please send samples of infested flower heads in sealed bags or containers with source information to: Entomology, RHS Garden Wisley, Woking, Surrey GU23 6QB
By Email: Alternatively, photos including postcode of location of the plant, will help us to map how widespread the midge is in the UK and can be emailed to firstname.lastname@example.org.
If the foliage of Agapanthus appears healthy but the flowers are abnormal in the ways described below, then agapanthus gall midge is most likely the cause:
Currently control measures attempt to interrupt the pest's life cycle:
The RHS is currently researching potential chemical and biological controls. As the larvae develop inside the plant tissue it is likely to be very difficult to target them with spray controls. The underground pupation and overwintering life stage may be a more useful target for control.
The tiny gall midge lays eggs on the plant and the larvae develop inside the individual flower buds, inside the flower head sheath or in the petals of flowers that have gone over. The larvae can then cause the bud to be deformed and discoloured and often fail to open, as their feeding activities convert the plant material into a gall. The severity of the damage can range from a couple of buds failing to collapse of the entire flower head.
Infestation can be confirmed by opening the buds or flower heads and looking for the presence of small maggots 1-3mm in length which are a creamy yellow colour. The midge larvae leave the flower head to pupate in the soil, which takes around ten days. It is likely that they also overwinter in the soil and pupate the next spring.
The larvae can live in any stage of flower development, including in senesced flowers. Larvae can most commonly be seen inside individual flower buds, but if infestation occurs before the flower head sheath opens then the larvae can live and feed between the developing flowers and cause complete failure of the flower head.
Our research so far has shown that there may be multiple overlapping generations of the midge, as active larvae have been seen between mid-June and early October. This means that focussed control may be difficult. The RHS is currently collaborating with ADAS in an AHDB funded research project to look at potential chemical and biological controls for the midge.
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